1. Field of the Invention
This invention relates in general to the generation and control of thermal aircraft, and especially of hot air inflatable balloons. In particular, the invention relates to improved venting means for venting or deflation of thermal aircraft and to thermal aircraft incorporating such venting means.
2. Description of the Prior Art
Thermal aircraft, such as hot air balloons, comprise an aerostat or an envelope having a top opening with a top cap for closing the opening, and a gondola suspended from the bottom of the envelope. During normal flight, the top opening is closed, but can be partially opened during flight for venting of hot air from the envelope for vertical maneuvering. At the end of the flight the top opening is fully opened to rapidly deflate the envelope.
Deflation of the envelope is an important factor in the control of the balloon or other thermal aircraft. It is necessary and desirable when the balloon lands to rapidly deflate the balloon so that the envelope will rapidly collapse thus preventing the balloon from being blown across the ground by the wind, which has been the cause of many serious ballooning accidents. In the past, rapid deflation has usually been achieved by means of one or more removable panels attached to the envelope by means of hook and loop fasteners such as "Velcro" or similar fastening means, or by means of a "parachute valve" temporarily closing and being removable from an aperture at the upper end of the balloon envelope.
The invention of the parachute vent or parachute valve for conventional parachutes is generally attributed to Rohulick, U.S. Pat. No. 2,404,659 published in 1946. Rohulick conceived the idea of a parachute wherein the main parachute canopy or umbrella included a relatively small auxiliary umbrella to control the opening of an aperture at the top of the main parachute canopy. This concept was subsequently adapted to the control of hot air balloons by Robert Noirclerc (French Pat. No. 2 253 654--see below) in 1973, and by Tracy Barnes in 1974 (not patented). See also U.S. Pat. No. 4,033,527 to Roger Parsons, published in 1976, wherein the adaptation of a parachute valve to hot-air airships is disclosed.
A parachute vent is typically an oversize circular panel manufactured from the same material as that used in the balloon envelope (e.g. high tenacity polyurethane coated ripstop nylon), held in place against the underside of the aperture in the top of the balloon by internal (hot) air pressure. The seal is a suction seal of fabric of the parachute against the fabric of the balloon envelope surrounding the perimeter of the aperture. In effect, the parachute acts as an operculum, and the parachute and associated aperture operate or act as an opercular or operculate valve.
The parachute normally seals and is seated against the balloon aperture, being appropriately centered against the aperture and/or within the balloon envelope by means of a plurality of centralising lines extending between the outer perimeter of the parachute and the inner walls of the envelope. A plurality of shroud lines depend downwardly from the perimeter of the parachute, joined together at a point centrally below the parachute, fitted with a pulley. A parachute activation cord passes through this pulley, tethered at one end to the inner wall or a seamed rib of the envelope towards the lower end thereof, with the other end of the activation cord extending to the operator, or balloon pilot, in the basket below the balloon envelope. In operation, if the pilot wishes to descend or to simply vent the balloon, the pilot pulls the activation cord downwardly, which pulls the parachute downwardly and away from the aperture, venting the balloon envelope to the atmosphere. As the pilot releases the downward pull pressure on the activation cord, the parachute is forced upwards by the internal pressure within the balloon such that the parachute seats against and seals the upper aperture of the balloon.
As the size of the hot air balloons have increased during recent years, the operation of parachute vents have become a problem for all but very heavy pilots. This problem is exacerbated during the balloon landing phase, since the force required to activate or to open the vent is increased during the landing phase, due to pressure from the escaping air which tends to force the parachute operculum vent back up against the aperture.
During the past two decades, numerous attempts have been made to improve the reliability of parachute-type vents or to improve the mechanical advantage in operating same. French Pat. No. 2 253 654 (Noirclerc), published in July 1975 and based on an application filed in France in December 1973, discloses a parachute vent for aerostats--including hot air balloons--wherein the vent is a double vent arrangement comprising a small inner parachute vent coaxially and concentrically aligned within a larger outer parachute vent, which in turn controls the closure of an aperture at the upper end of the envelope of a hot air balloon. The small vent is opened first, followed by the opening of the larger vent for precise and rapid deflation of the envelope.
U.S. Pat. No. 4,651,956 to James Winker et al, granted March 1987, discloses a hot air balloon having a top cap or closure valve which forms both a deflation panel and a maneuvering port for the balloon. The top cap is releasably secured to the balloon envelope by means of a closure assembly including a fixed member secured to the envelope interior and a releasable member which is firstly secured to the top cap and secondly releasably secured to the fixed member. However, once released it is not possible to re-set the top cap in flight, or to terminate or reverse the deflation process once it has been commenced.
U.S. Pat. No. 4,836,471 to Donald Piccard, granted June 1989, discloses a parachute-type vent for hot air balloons which may be opened by applying force to a pull cord having a series of pulleys whereby the applied force is provided with an improved mechanical advantage. In one embodiment, the closure valve is provided with a reefing line to choke the closure valve radially inwardly to open the balloon aperture for rapid deflation of the balloon. However, again it is not possible to reset the valve in flight or to reverse or terminate the deflation process once it has been commenced.
British patent publication No. GB 2260956A in the name of Cameron Balloons Limited (inventor Donald A. Cameron), published in May 1993, discloses a venting valve for a hot air balloon having a valve member which may be secured to the envelope by a releasable locking mechanism to limit the valve-opening movement of the valve member. In this venting valve, with the valve member secured to the envelope by the locking mechanism, the valve member is prevented from moving clear of the balloon aperture. This is suitable for in-flight venting of the balloon envelope since the valve can be readily opened and closed in flight. For rapid deflation of the balloon envelope, the locking mechanism is released and the valve member moves to a position well clear of the balloon aperture allowing increased outflow of air. However, when the locking mechanism has been released, it is not possible to reset the valve member in place during flight.
Also within the last few years another attempt has been made to improve the parachute vent, by the development of the so-called `SuperChute` in the United Kingdom by Lindstrand Balloons Limited (designed by Per Lindstrand and Simon Forse - patent particulars not known). As in the case of a conventional parachute vent, the SuperChute comprises a circular panel which seals against the balloon aperture. It may also have shroud lines from its perimeter joined centrally below the circular panel such that it can be operated like a conventional parachute vent. However, it also comprises a control rope attached to the axial center of the circular panel of the SuperChute (or to a plurality of ropes which extend radially from the center of the circular panel to the outer perimeter thereof). The SuperChute is also characterised by the rerouting of the parachute valve centering lines back up to the crown of the balloon envelope where they are held in place by an armed release mechanism or locking device which must be "fired" before actuating the rapid deflation mode. Before activation the SuperChute behaves as a typical pulley-assisted parachute valve either for in-flight venting or for final deflation in moderate wind speeds.
The SuperChute is operated by two lines, one is the arming line and the other is the final deflation line. Until the arming line is pulled, the SuperChute cannot be activated. Once armed the system is ready to activate, but it still allows the pilot to operate it similar to a conventional parachute valve. When the pilot wishes to rapidly descend or to deflate the balloon, he pulls downwardly on the central control rope which causes the parachute valve canopy to gather radially inwardly and downwardly into the balloon center, in effect forming a plume or to `roman candle` the parachute. The overall effect is to rapidly open the balloon aperture to vent the hot air in the envelope to the atmosphere, causing the balloon to descend and to rapidly deflate. The SuperChute requires much less physical pressure or exertion to operate than does a conventional parachute vent, but it has a disadvantage in that it is not possible to reverse or to reset the SuperChute valve during flight once it has been activated, since resetting is normally carried out from outside the balloon envelope after landing procedures or before embarking on a new flight.
It is an object of this invention to provide improved venting means for the generation and control of thermal aircraft such as inflatable balloons, and especially hot air balloons.
It is another object of this invention to provide improved venting means for thermal aircraft which go at least some way towards overcoming or at least minimising the prior art problems or limitations outlined above.
It is a further object of this invention to provide improved venting means for thermal aircraft which is universally adaptable for use with any type of thermal aircraft which requires venting of an internal chamber or envelope to the atmosphere.
It is yet another object of this invention to provide improved venting means for thermal aircraft which is relatively simple and inexpensive to manufacture, and which is simple in operation.
It is yet a further object of this invention to provide thermal aircraft which comprise venting means of the type disclosed herein.
Other and further objects of the present invention will become apparent to those skilled in the art upon a study of the following description, appended claims and accompanying drawings.